Hope this is the right forum for this. I am reading a seminal "mathematical biophysics" paper from 1943 by MucCulloch and Pitts, and I got into a little bit of a rabbit hole trying to understand this equation in old-style logical notation.
By following this link, I think I got most of it figured out, and I'm assuming
x’) means "predecessor of x", and so the equation should be read as something like "The property S(P) holds for t if and only if P holds for Kx and t is the predecessor of x? But what does Kx mean? Doesn't this equation fulfill the definition if Kx were just replaced by x in the definition?
Thanks for any guidance on this!